[PATCH v3 2/2] Make editenv chase symlinks including those across devices

[Javier Martinez Canillas]

From: Peter Jones <address@hidden>

The grub-editenv create command will wrongly overwrite /boot/grub2/grubenv
with a regular file if grubenv is a symbolic link. But instead, it should
create a new file in the path the symlink points to.

This lets /boot/grub2/grubenv be a symlink to /boot/efi/EFI/fedora/grubenv
even when they're different mount points, which allows grub2-editenv to be
the same across platforms (i.e. UEFI vs BIOS).

For example, in Fedora the GRUB EFI builds have prefix set to /EFI/fedora
(on the EFI System Partition), but for BIOS machine it'll be /boot/grub2
(which may or may not be its own mountpoint).

With this patch, on EFI machines we can make /boot/grub2/grubenv a symlink
to /boot/efi/EFI/fedora/grubenv, and the same copy of grub-set-default will
work on both kinds of systems.

Signed-off-by: Peter Jones <address@hidden>
Signed-off-by: Jonathan Lebon <address@hidden>
Reviewed-by: Adam Jackson <address@hidden>
Signed-off-by: Javier Martinez Canillas <address@hidden>

---
Daniel,

I didn't add a check for x* allocation functions since as mentioned in my
previous email these are not needed. The functions already check for NULL
and call exit(3) if that's the case.

Changes in v3:
- A couple of style cleanups.

Changes in v2:
- Address issues pointed out by Daniel Kiper in the previous version.

 Makefile.util.def | 11 +++++++++
 util/editenv.c    | 59 +++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 68 insertions(+), 2 deletions(-)

diff --git Makefile.util.def Makefile.util.def
index 969d32f0097..733a397cb2b 100644
--- Makefile.util.def
+++ Makefile.util.def
@@ -240,8 +240,19 @@ program = {
 
   common = util/grub-editenv.c;
   common = util/editenv.c;
+  common = util/grub-install-common.c;
   common = grub-core/osdep/init.c;
+  common = grub-core/osdep/compress.c;
+  extra_dist = grub-core/osdep/unix/compress.c;
+  extra_dist = grub-core/osdep/basic/compress.c;
+  common = util/mkimage.c;
+  common = util/grub-mkimage32.c;
+  common = util/grub-mkimage64.c;
+  common = grub-core/osdep/config.c;
+  common = util/config.c;
+  common = util/resolve.c;
 
+  ldadd = '$(LIBLZMA)';
   ldadd = libgrubmods.a;
   ldadd = libgrubgcry.a;
   ldadd = libgrubkern.a;
diff --git util/editenv.c util/editenv.c
index eb2d0c03a98..ce00da3fc1b 100644
--- util/editenv.c
+++ util/editenv.c
@@ -28,15 +28,19 @@
 
 #include <errno.h>
 #include <string.h>
+#include <libgen.h>
 
 #define DEFAULT_ENVBLK_SIZE    1024
 
 void
 grub_util_create_envblk_file (const char *name)
 {
+  int rc;
   FILE *fp;
   char *buf;
   char *namenew;
+  ssize_t size = 1;
+  char *rename_target = xstrdup (name);
 
   buf = xmalloc (DEFAULT_ENVBLK_SIZE);
 
@@ -60,7 +64,58 @@ grub_util_create_envblk_file (const char *name)
   free (buf);
   fclose (fp);
 
-  if (grub_util_rename (namenew, name) < 0)
-    grub_util_error (_("cannot rename the file %s to %s"), namenew, name);
+  while (1)
+    {
+      char *linkbuf;
+      ssize_t retsize;
+
+      linkbuf = xmalloc (size + 1);
+      retsize = grub_util_readlink (rename_target, linkbuf, size);
+      if (retsize < 0 && (errno == ENOENT || errno == EINVAL))
+        {
+          free (linkbuf);
+          break;
+        }
+      else if (retsize < 0)
+        {
+          free (linkbuf);
+          grub_util_error (_("cannot rename the file %s to %s: %m"), namenew, 
name);
+        }
+      else if (retsize == size)
+        {
+          free (linkbuf);
+          size += 128;
+          continue;
+        }
+
+      linkbuf[retsize] = '\0';
+      if (linkbuf[0] == '/')
+        {
+          free (rename_target);
+          rename_target = linkbuf;
+        }
+      else
+        {
+          char *dbuf = xstrdup (rename_target);
+          const char *dir = dirname (dbuf);
+
+          free (rename_target);
+          rename_target = xasprintf ("%s/%s", dir, linkbuf);
+          free (dbuf);
+          free (linkbuf);
+        }
+    }
+
+  rc = grub_util_rename (namenew, rename_target);
+  if (rc < 0 && errno == EXDEV)
+    {
+      rc = grub_install_copy_file (namenew, rename_target, 1);
+      grub_util_unlink (namenew);
+    }
+
+  if (rc < 0)
+    grub_util_error (_("cannot rename the file %s to %s: %m"), namenew, name);
+
   free (namenew);
+  free (rename_target);
 }
-- 
2.21.0